1. Field of the Invention
The present invention relates generally to a steam cooled system in a combined cycle power plant, and more specifically to one constructed such that a high temperature portion (a portion to be cooled) of a gas turbine combustor in a combined cycle power plant, in which a gas turbine plant and a steam turbine plant are combined together, is cooled by steam coming from a waste heat recovery boiler.
2. Description of the Prior Art
In a combined cycle power plant in which a gas turbine plant and a steam turbine plant are combined together, a high temperature range of the thermal energy is taken charge of by a gas turbine and a low temperature range thereof by a steam turbine, respectively, so that the thermal energy is recovered and used effectively. Hence great attention has been recently paid to this power system.
In this combined cycle power plant, as one measure for enhancing the efficiency, in place of using air as a cooling medium for cooling the gas turbine high temperature portion, a system using steam generated in the bottoming cycle is being disclosed.
FIG. 3 shows a prior art gas turbine steam system in a combined cycle power plant. In FIG. 3, numeral 1 designates a gas turbine, numeral 2 designates a waste heat recovery boiler thereof, numeral 3 designates a high pressure steam turbine and numeral 4 designates an intermediate pressure steam turbine. The waste heat recovery boiler 2 comprises a high pressure drum 5, a high pressure superheater 6, a reheater 7, an intermediate pressure drum 9, an intermediate pressure superheater 10, etc.
Numeral 8 designates a high temperature portion (or a heat exchanger therefor) of a gas turbine combustor etc., which is a portion to be cooled by steam.
Numeral 12 designates a temperature control valve, which is controlled by a temperature control device 11. Numeral 13 designates a superheater outlet steam temperature detector and numeral 15 designates a high temperature portion outlet steam temperature detector.
In the gas turbine steam system shown in FIG. 3, exhaust gas of the gas turbine 1 is led into the waste heat recovery boiler 2. Steam from the high pressure drum 5 of the waste heat recovery boiler 2 is led into the high pressure steam turbine 3 via the high pressure superheater 6. Also, steam from the intermediate pressure drum 9 is led into the intermediate pressure steam turbine 4 via the intermediate pressure superheater 10 and the reheater 7 sequentially. Outlet steam of the high pressure steam turbine 3 joins in an inlet steam of the reheater 7.
On the other hand, outlet steam of the intermediate pressure superheater 10 diverges partly from that led to the reheater 7 to sequentially flow through the temperature control valve 12 and the high temperature portion 8 of the gas turbine combustor and then joins the outlet steam of the reheater 7 to be led into the intermediate pressure steam turbine 4.
Output of the high temperature portion outlet steam temperature detector 15, which is provided at an outlet of the high temperature portion 8, is sent to the temperature control valve 12, which is provided in a steam line on an inlet side of the high temperature portion 8 via the temperature control device 11.
Thus, the exhaust gas of the gas turbine 1 enters the waste heat recovery boiler 2 to generate a high pressure steam, an intermediate pressure steam and a low pressure steam. The steam generated at the high pressure drum 5 becomes superheated steam at the high pressure superheater 6 to work at the high pressure steam turbine 3 and then flows through a high pressure exhaust steam line to join in the intermediate pressure steam and then is reheated at the reheater 7 to be led into the intermediate pressure steam turbine 4. Steam generated at the intermediate pressure drum 9 is superheated at the intermediate pressure superheater 10 and is led in a necessary amount to the high temperature portion 8 of the gas turbine 1 combustor etc. for cooling thereof, either through a heat exchanger or directly in the high temperature portion 8, and then joins in the outlet steam of the reheater 7. Surplus steam joins in the steam coming from the high pressure steam turbine 3 through the high pressure exhaust steam line to be led to the reheater 7.
As to the steam which has passed through the high temperature portion 8, the temperature thereof is controlled such that the temperature control valve 12, which is provided in the steam line on the inlet side of the high temperature portion 8, is controlled by a control signal from the high temperature portion outlet steam temperature detector 15 and the temperature control device 11 so that the flow rate of the steam is controlled.
The prior art steam cooled system is a system in which the steam used for cooling of the high temperature portion 8 of the gas turbine combustor etc. is controlled in flow rate by the temperature control valve 12 provided at an inlet of the high temperature portion 8 so that the outlet steam temperature of the high temperature portion 8 is set to a predetermined value.
In this case, if a cooling steam pressure becomes lower than the pressure in a turbine cylinder of the gas turbine 1 (discharge pressure of gas turbine air compressor), combustion gas comes into the steam system and there arises a fear of the occurrence of problems, such as burning of the steam system etc.
That is, in the prior art system in which the temperature control valve 12 is provided at the inlet of the high temperature portion 8, while it is possible to control to suppress the rise of the outlet steam temperature of the high temperature portion 8, there is a problem in that it is difficult to control in the case where the cooling steam pressure becomes lower than the pressure in the turbine cylinder (the discharge pressure of gas turbine air compressor).
Also, in the prior art steam cooled system in the combined cycle power plant, while a basic framework of the control of the gas turbine operation is maintained such that the gas turbine is operated safely by a fuel flow control valve being controlled by a valve opening command signal, which is made by the lowest value of the fuel flow rate command signals given from a speed governing device (output control device), a combustion temperature control device, a load limit control device and an acceleration control device, there is no sufficient signal of flow rate control of the cooling steam for cooling the high temperature portion of the gas turbine.
That is, in the gas turbine employing the steam cooled system, as there is a need to prevent unusual excess cooling or heating and to suppress the occurrence of thermal stress at the gas turbine high temperature portion, it is necessary to control the steam supply rate so as to effect an appropriate cooling corresponding to the thermal load at the gas turbine high temperature portion.